Hey....I am having the exact same issue (relieved to see other people in this forum having the issue, which seems to imply its not necessarily a specific hardware issue to one car)...
After upgrading to 8.1, my autopilot stopped working. Even cruise control doesn't work.I would get the same "Cruise not available" message. On occasions I did get the message "Obstacle in path". Not sure what that meant.
I took my car to the SC, they reset my calibration and told me that I should drive it for few days. For the first 50 miles, it would get the message "Camera is calibrating..". After 50 miles, it stopped giving me the message, but autopilot still doesn't work! The SC advised me to come back after two weeks of driving. They seem to think its still calibrating.
I got my Model X Late December 2016. When did you guys get yours? I also wonder why it would take so much longer for some model X to calibrate while it took less time for others. I drive in roads with good lane markings. Prior to 8.1, my autopilot worked fine.